To realize highly integrated ultrafine semiconductor devices developing in half pitch from 65 nm to 45 nm, in photolithography, as high-resolution technologies in exposure equipment, developments of various technologies such as a high-NA technology using a projector lens with high numeric aperture, an immersion exposure technology for exposure with a highly-refractive medium between a projector lens and a target of exposure, and an exposure technology with deformed illumination have been rapidly advanced.
On the other hand, as measures of improving resolution in a photomask (also referred to as a reticle) used for lithography, with miniaturization and higher precision of a conventional binary mask consisting of a part that passes light and a part that blocks light, developments and practical use of phase shifting masks such as a Levenson type (also referred to as Levenson-Shibuya type) phase shifting mask intended for improvement in resolution by phase shifting effect utilizing light interference, a halftone type phase shifting mask consisting of a part that transmits light and a part that semi-transmits light, a chromeless type phase shifting mask with no light shielding layer of chrome or the like are being advanced.
In the photolithography technology, since the minimum dimensions (resolution) that can be transferred by projection exposure equipment is proportional to the wavelength of light used for exposure but inversely proportional to the numeric aperture (NA) of a lens of a projection optical system, the wavelength of the exposure light is being shorter and the NA of the projection optical system is made higher upon request for miniaturization of semiconductors. However, the shorter wavelength and the higher NA have limitations for fulfilling the request.
Accordingly, to raise the resolution, super-resolution technologies for realizing miniaturization by reducing the value of process constant kl (kl=(resolution line width)×(numeric aperture of projection optical system)/(wavelength of exposure light)) have been recently proposed. As such super-resolution technologies, there are methods such as a method of optimizing a mask pattern by providing a supplementary pattern and a line width offset to the mask pattern according to the property of the exposure optical system, and a method called a deformed illumination method (also referred to as a grazing-incidence method). For the deformed illumination method, typically, orbicular zone illumination using a pupil filter, double-pole (also referred to as two-pole, two-point, or dipole) illumination and quadruple-pole (also referred to as four-pole, four-point, or quadrupole) illumination, etc. are used.
Further, in the photolithography technology for transferring a pattern using a photomask, it is also known that there is a predetermined polarization state for preferably imaging a pattern on a wafer.
As described above, in photolithography with a half pitch of 60 nm or less, a photolithography technology using an ArF excimer laser as an exposing source for immersion exposure with a high-NA lens has a high degree of expectation. However, there is a problem that, even with the same process constant kl, the imaging performance is degraded and the contrast of an optical image within a photoresist (hereinafter, referred to as within resist) on a wafer is lowered due to a problem that the polarization dependency called “vector effect” by the high-NA optical system becomes significant, and a fine pattern of the photoresist on the wafer is not resolved (e.g., see Patent Document 1).
For instance, FIG. 13 shows a relationship between the optical image contrast of a conventional binary mask or halftone type phase shifting mask and a bias as a correction value of a space part of the mask pattern, which will be described later. As shown in FIG. 13, the optical image contrast takes a value of 0.580 at the maximum for the conventional halftone type phase shifting mask (indicated by a broken line HT), and a value of 0.612 at the maximum for the conventional binary mask (indicated by a solid line BIM).
To address the problem of the lower optical image contrast within resist due to higher NA, in the photomask, a method of changing a photomask material and a three-dimensional structure such as a cross-sectional shape of a photomask pattern (hereinafter, referred as mask pattern) or the like is considered.
However, in the photolithography with a half pitch of 60 nm or less, there are problems that various parameters relating to the optical image contrast within resist have complex relationships, demonstrations by experiments are difficult because of ultrafine pattern, and a parameter of the photomask having a great effect on the contrast improvement and a photomask structure based thereon are not easily found.
Patent Document 1: JP-A-2004-111678